Recently, in order to improve tire performance during high speed running, spiral belts are widely used in radial tires, especially four-wheeled vehicle tires, e.g. passenger car tires.
In a motorcycle tire, the tread and carcass have curved profiles with a relatively small radius of curvature in comparison with four-wheeled vehicle tires. Therefore, a belt to be disposed between the tread and carcass must have a curved profile with a small radius of curvature.
To make a spiral belt for such motorcycle tire, a belt cord must be spirally wound on a curved face which is generally the radially outer surface of the carcass. Therefore, the windings are liable to be dislocated.
On the other hand, in order to obtain a desired belt effect, the cord count is varied. If spaces are provided between the windings to adjust the cord count, the windings are easily dislocated and loosened. Thus, the cord winding operation is very difficult. Even if such dislocation and looseness could be avoided, the cord spacings are liable to be disturbed during the tire building operation, and accuracy can not be achieved, and thereby high speed performance can not improved.
In the conventional spiral belts, therefore, to avoid such problems, a belt cord (a) is wound compactly, that is, without cord spacings as shown in FIG. 8. In this case, the cord count is determined by only the cord diameter. Therefore, to adjust belt characteristics, the material, denier, twist and/or structure of the belt cord itself have to be changed. As a result, the adjustable range and the design freedom are restricted.